Cutting and sealing plastic tubes

ABSTRACT

In a blow molding operation wherein a thermoplastic parison is closed off at one end and thereafter expanded by the introduction of internal fluid pressure to conform to a mold, the tube is sealed and severed by simultaneously forcing the walls of the tube together along at least three different paths which converge toward a central point. This sealing means is particularly useful in sealing thermoplastic parisons which have been cooled and thereafter reheated to a temperature near but below the crystalline melting point of the thermoplastic material.

' United States Patent Turner *Oct. 17, 1972 [54] CUTTING AND SEALINGPLASTIC 2,974,367 3/1961 Doering et a1. ..65/299 X TUBES 3,311,6843/1967 Heider ..264/98 X 3,311,949 4/1967 Moran ..'...264/98 X [72],Invent g 's' 3,382,532 5/1968 Schweiger ..264/94 x a 3,390,426 7/1968Turner et al. ..264/98 X 73 Assi nee: Philli sPetroleum Com an g h p f py FOREIGN PATENTS OR APPLICATIONS N t T t' t t f t 1 i fzt gg f zg f gg943,573 12/1963 Great Britain ..264/98 has been dsclalmed' I PrimaryExaminer-Robert F. White [22] Filed: June 27, 1969 Assistant Examiner-J.H. Silbaugh [21] Appl' No; 837,128 Attorney-Young and Quigg Related US.Application Data ABSTRACT 2 Division f Sen 5 5 910 21 19 In a blowmolding operation wherein a thermoplastic Pat 3,478,388 parison isclosed off at one end and thereafter ex:

panded by the introduction of internal fluid pressure 52 U.S. c1,..264/98, 264/150 264/163 conform a the tube is Sealed and Severed 51Int. Cl. ..B29c 17/07 B296 17/10 by simultanewsly facing the Walls thetube [58] Field of Search U 264/94 98 5 together along at least threedifferent paths which 18/5 i f 5 converge toward a central point. Thissealing means is particularly useful in sealing thermoplastic parisonswhich have been cooled and thereafter reheated to a [56] References cuedtemperature near but below the crystalline melting UNITED STATES PATENTSpoint of the thermoplastic material.

3,399,424 9 9/1968 Sheptak ..264/94 4 Claims, 8 Drawing Figures PATENTEDv 3,699,201

sum 1 or 4 Sch/ INVENTOR. E.W. TURNER BY W LQAL A TTORNE Y5 PATENTEUUBI1 1 m2 SHEET 2 OF 4 INVENTOR.

E.W. TURNER Y 1 4. B Q 72 A T TORNE VS PATENTEnncmaszz 3.699.201

SHEET 3 0F 4 INVENTOR.

E.W. TURNER ATTORNEYS CUTTING AND SEALING PLASTIC TUBES This applicationis a division of copending application, Ser. No. 595,910, filed Nov. 21,1966, now U.S. Pat. No. 3,478,388.

This invention relates to cutting and sealing plastic tubes. In anotheraspect, this invention relates to a novel process for cutting andsealing parisons employed in the manufacture of hollow plastic articlesby blow molding.

The most common technique used to form hollow plastic articles is blowmolding. In one such technique, a molten parison of plastic materialextrudes from an annular die between a two part (split) blow mold whichcloses together about the parison, pinching off and sealing the open endthereof along a single line where the two mold sections meet, and afluid is introduced into an enclosed parison to expand and shape theparison to the mold cavity.'ln another blow molding technique a tubularthermoplastic plastic parison which has been cooled to below itscrystalline freeze point and then heated to a temperature near to butbelow its crystalline melt point, and which is still in a predominantlycrystalline condition, is supported on one end by a gripping means,which may also be a forming means,

with a centrally located blowing tube, and is placed between a two part(split) blow mold which closes together about the parison, sealing andpinching off the open end thereof along a single line as describedabove. This type of pinching off and sealing operation substantiallyflattens the closed end of the parison and causes a mass of polymer toaccumulate at the ends of the pinch off line due to the walls of theparison being forced towards the ends of the line. This results in thickareas at the ends and thin areas between the ends of the pinch off line,which in turn results in a weaker area of seal between the ends of thepinch off line. This weaker seal area contributes to container wallweakness and consequent premature failure on drop impact. This weakerseal has particularly been a problem where the seal is attempted in thepredominantly crystalline parisons mentioned above. Another conventionalmethod of cutting and sealing a parison is to utilize a one way nip-off,which in effectutilizes shearing force against one side of the heatedtube to force that side of the parison wall against the other side andthereby seal the sides together before the leading end of the parison ispinched off. This method results in a rather large area of the parisonwall directly affected by-the seal, and relatively large ears or flangesthat appear at the ends of the nip-off line and detracts somewhat fromthe appearance of the completed article. Therefore, it is highlydesirable to have a method of cutting and sealing parisons that willminimize the area which is directly af fected by a single direction ofseal, and at the same time complete a seal in which the plastic walls inthe area of the seal have no resulting thin areas of wall thicknessalong the line of seal.

Accordingly, one object of this invention is to provide a novel methodfor cutting and sealing plastic tubes.

Another object of this invention is to provide a method for obtainingimproved hollow plastic articles.

A further object of this invention is to provide a novel method forcutting and sealing a heated thermoplastic parison, and to therebyincrease the strength of the seal by obtaining uniform distribution ofthe plastic over the seal area.

Other objects and advantages of this invention will be apparent to oneskilled in the art from a study of this disclosure.

According to the invention, the walls of a heated thermoplastic tube areforced together from at least three directions to thereby form a sealhaving a multi-' line configuration. The walls are then pinched offbelow the seal line to yield a sealed parison. This multidirectionalforce is attained by at least three cutting and sealing jaws, acting inconcert and closing together about the parison toward a central point.

According to one embodiment of this invention, a novel split sectionblow molding apparatus is provided whereby the leading portion of aheated thermoplastic parison is sealed in at least three directions andthen pinched off by at least tree cutting and sealing jaws mechanicallyactivated to close about, seal and then cut the said leading portion ofthe heated parison when the split sections of the blow molding apparatusare forced together.

According to another embodiment of this invention, a novel tube sealingapparatus is provided whereby an open end of a heated thermoplastic tubeis sealed in at least three directions and then pinched off by at leastthree cutting and sealing jaws that are mechanically activated to closeabout, form a seal having a multi-line configuration and then pinch offthe said end of the thermoplastic tube.

This invention can better be illustrated by a study of the drawings inwhich:

FIG. 1 is a vertical section of a split blow molding device having aparison sealing and cutting apparatus of this invention attachedthereto.

FIG. 2 is a view partially in section of the parison sealing and cuttingdevice of FIG. I having four sealing and cutting jaws in open positionwith suitable activating means.

FIG. 3 is a plan view of the apparatus of FIG. 2 showing the sealing andcutting jaws in closed position and the activating means fully engaged.

FIGS. 4-6 illustrate the action of the sealing and cutting jaws whenforming a multi-directional seal.

FIG. 7 is a sectional view of another embodiment of this inventionshowing a tube sealing and cutting device that is hydraulicallyactivated.

FIG. 8 is a plan view of the apparatus of FIG. 7.

Now referring to FIG. 1, there is illustrated a sectional view of abottle blow molding apparatus compris ing sections 1 and 2 with theparison sealing and cutting device sections 3 and 4 operatively attachedthereto. Sealing and cutting sections 3 and 4 are attached to moldsections 1 and 2 by bolts represented by 5 and 6, respectively. Plate 7is interconnected between section 3 and mold section I, and plate 8 isinterconnected between section 4 and mold section 2. Tubularthermoplastic parison 10, which has been heated but is in apredominantly crystalline condition, is clamped between jaws 9 andmember 11. The exterior portions then pinch off the portion below theline of seal when sections 1 and 2 are moved together. As illustrated,the upper portions of sliding blocks and 16 are in slidable contact withplates 7 and 8 at points 7a and 8a, respectively. The lower portions ofsliding blocks 15 and .16 rest in grooves 17 and 18 of base members 19and 20, respectively. The underside of sealing and cutting jaw 13 forms.cutout 21 and the underside of sealing and cutting jaws 14 forms cutout22 for receiving excess parison. Concave surfaces 23 and 24 defineone-half of the. lower portion of the mold cavity when the mold is inclosed position. Lever arm 27 carrying roller 28 is connected to theouter end of base member and lever arm .25 carrying roller 26 isconnected to mold section 1 at a point above the place where plate 7intersects with mold section 1. As sections 1 and 2 close, rollers 26and 28 contact pressure bearing surfaces on sliding blocks 16 and 15,respectively, to cause sliding blocks to slide laterally in grooves 17and 18. The pressure bearing surfaces on sliding blocks 16 and 15 areheld against rollers 26 and 28 during the closing operation by theaction of compressive springs around guide rods 29 and 30 containedwithin conduits 31 and 32, respectively.

The construction and operation of sealing and cutting sections 3 and 4are illustrated in FIGS. 2 and 3.

Referring to FIG. 2 in detail, there is shown sections 3 and 4 of aparisonsealing and cutting apparatus normally attached to the bottomportion of a split mold apparatus as shown in FIG. 1. Apertures 5athrough base member 19, and apertures 6a through base member 20 areprovided as receptacles for connecting bolts 5 and 6, respectively thatsecure the cutting device to the respective mold sections. Sealing andcutting jaws 13, 13a, 14, and 14a are shown aligned in open position forreceiving a heated thermoplastic tube. As shown, sealing and cuttingjaws 13, 13a, 14 and l4acomprise the interior leading portions'ofsliding blocks 15, 15a, 16, and 16a, respectively. The bottom portionsof sliding blocks 15 and 15a fit in slidable contact grooves in basemember 19 and the bottom portions of sliding blocks 16 and 16a fit inslidable contact in grooves on base member, 20. The elements of slidingblocks 15, 15a, 16' and 16a as illustrated in FIG. 2 comprise: sealingand cutting jaws 13, 13a, 14 and 14a, respectively; pressure bearingsurfaces 37, 37a, 38 and 38a, respectively; and concave surfaces 23,23a, 24 and 24a, respectively. Sliding blocks 13 and 13a are shownpartially in section to illustrate conduits 31 and 39, respectively,extending therethrough.

Guide .rod 29 and compressive spring 33 are contained within conduits 31and 39 in sliding blocks 15 and 15a, respectively. Guide rod 30 andcompressive spring 36 are contained within similar conduits throughsliding blocks 16 and 160. Guide rod 29 rests on guide plug 34.Containing plug having driving groove 35a is screwed into the threadedportion 41 of conduit 39 within sliding block 15a. Conduit 31 withinsliding block 15 narrows in diameter at point to provide a stop forspring 33. The action of compressive spring 33 upon stop 40 will tend toforce sliding blocks 15 and 15a apart at all times. Lever arms 25a and27 having rollers 26a and 28 are connected to base members 19 and 20,respectively. Lever arms 25 and 27a having rollers 26 and 28a areconnected to the upper portion of a respective mold section in amannernot shown in FIG. 2.

Thus, in the operation of the device, sections 3 and 4 are forcedtogether causing rollers 26, 26a, 28 and 28a to contact pressure bearingsurfaces 38, 38a, 37 and 37a, respectively. As more force is applied tosections 3 and 4, the rollers will tend to roll on the respectivebearing surfaces and force the sliding blocks together in the grooves inthe respective base members thereby causing compressive springs 33 and36 to contract.

Sections 3 and 4 are shown in closed position in FIG. 3. Rollers 26,26a, 28 and 28a.are shown in contact with pressure bearing surfaces 38,38a, 37 and 37a, respectively. Compressive springs 33 and 36 (not shown)are fully compressed and sealing and cutting jaws 13, 13a, 14 and 14aare aligned in closed position. Concave surfaces 23, 23a, 24 and 24a areshown aligned in'closed position to thereby define the lower portion ofthe mold cavity.

The action of the sealing and cutting jaws in forming themultidirectional seal is shown by FIGS. 4-6 which are diagrammaticillustrations showing the various configurations of the thermoplastictubular wall section during the seal forming and pinching off operation.Referring now to FIG. 4, as sealing and cutting jaws on sliding blocks24, 24a, 23 and 23a travel along the paths as illustrated by the arrowswhich are substantially perpendicular to and have points of convergencenear the longitudinal axis of tube 10, the walls of tube 10 are forcedinwardly at points P.

FIG. 5 illustrates the position of points P when the sealing and cuttingjaws are in the half closed position. It will be noted, that as the tubewalls are being forced together, there is a uniform stretching of thetube'walls around the circumference near points P and C. This actionwill result in a seal near the longitudinal axis of the tube havinguniform wall thickness in the wall sections that are sealed together.

FIG. 6 illustrates seal S formed as the sealing and cutting jaws come tothe closed position. The tube walls are forced together in eightdirections by the action of the four sealing and cutting blockstraveling along four different paths to the common junction near theiongitudinal axis of the tube. The, action of the sealing and cuttingjaws converging will also pinch off the lower portion of tube 10 fromthe resulting sealed upper portion. It can readily be seen that in thismethod of sealing parisons wherein adjacent wall sections are stretchedand forced together near the longitudinal axis of the parison, theparison wall area which is directly affected by a single direction ofseal is minimized, and at the same time a seal is effected betweenadjacent parison walls of uniform thickness. Bottles formed fromparisonssealed in this manner exhibit substantially higher base strengthand a lower failure rate upon drop impact than containers having basessealed by the one way or two way nip-off method.

FIG. 7 is a sectional view along line 7-7 of FIG. 8 which is a top viewof another embodiment of this inventionshowing a hydraulically activatedtube cutting and sealing device. This device is similar to the one shownin FIGS. l3 except that it operates independently of a moldingapparatus, and is used to cut and seal thermoplastic tube sections.Thermoplastic tube sections cut and sealed by this embodiment can beused as preformed parisons for use in blow molding, containers, or foruse in fluid piping operations. Referring now to FIG. 7, sliding blocks115 and 116 in this embodiment are similar to the sliding blocks and 16in the device of FIGS. 1-3 except upper portions of sliding blocks 115and 116, respectively, are adapted to fit in slidable contact similarlyto lower portions thereof within body members 119 and 120, respectively,and the concave portions which cooperate to define the lower portions ofthe mold device are eliminated. Guide rods 129 and 130 having springsthereon are inserted in conduits within sliding blocks 115 and 116 in asimilar manner as guide rods 29 and 30 within sliding blocks 15 and 16of FIGS. l3. Body members 119 and 120 have also been modified tocooperate with modified blocks 115 and 116. As shown, body member 119supports lever am 125, and body member 120 supports lever arm 127.Section 104 is shown in stationary position, and section 103 is movablein response to the motion of piston rod 100 of hydraulic cylinder 102.

As stated, FIG. 8 is a top view of this embodiment comprising sections103 and 104 and hydraulic 100 operatively attached thereto. Guide rails101 fit within grooves on the underside of section 103.

Thus, in the operation of this device, a heated plastic tube is placedbetween sections 103 and 104. Hydraulic piston rod 100 is activated toforce section 103 toward section 104, this movement being guided byguide rails 101. Rollers 126, 126a, 128 and 128a then contact pressurebearing surfaces 138, 1380, 137 and 137a, respectively, and furtherlateral movement of section 103 causes sealing and cutting jaws 113 and1l3a'on sliding blocks 115 and 115a and sealing and cutting jaws 114 and114a on sliding blocks 116 and 116a to move together. Therefore, themovement of section 113 toward section 104 coupled with the inwardmovements of cutting and sealing jaws 113, 113a, 114, 114a will cut andseal the hot thermoplastic tube located therebetween. It must be notedthat the use of one hydraulic cylinder as shown in FIGS. 7 and 8 is notintended to limit the scope of this invention. This device can operatewith two movable sections operated by two hydraulic cylinders ormechanical screws or mechanical levers, or in any suitable manner thatwill force the respective sections together. Also, the deviceillustrated in FIGS. 7 and 8 can be used to cut solid thermoplasticmaterial in the form of round or octagonal rods, but the device has itsgreatest utility in cutting and sealing hot thermoplastic tubularobjects because the resulting'seal will have a multi-line configurationwith no uneven thick or thin stressed areas therein.

It must be noted that the particular devices illustrated in FIGS. 1-3and 7--8 are not intended to limit the scope of this invention. Thedrawings illustrate the cutting device having two sections and twomovable blades in each section; however, variations can be made fromthis without departing from the scope of this invention. For example,this device is operable when only one of the cutting sections hasmovable blades therein and th other section has one non-movable blade.This con iguration would be used where a threeway nip-off is required.Also, several movable blades can be utilized in any one section. Forexample, guide rod 29 or 30 can extend through three or more movableblocks, with individual compressive spring means thereon and separatingeach individual movable block. For example, when utilizing three movableblocks in a mold section, a compressive spring means will be placedbetween the first and second blocks and a second compressive springmeans will be placed between the second and third blocks.

What is claimed is:

1. In a method of blow molding hollow articles by forming a heatedthermoplastic tubular parison, sealing and pinching off an open end ofsaid parison, and expanding said parison to conform to the shape of amold cavity, the improvement comprising: performing said sealing andsevering operation by simultaneously applying pressure radially inwardfrom at least three sharp points thus forcing the walls of said heatedthermoplastic tubular parison together along at least three differentpaths substantially perpendicular to and which have a common junctionnear the longitudinal axis of said heated thermoplastic tubular parisonto thereby obtain a seal having a multi-line configuration, andcontinuing the force along said paths until the lower portion of saidheated thermoplastic tubular parison is pinched off from the resultingsealed upper portion.

2. The method of claim 1 wherein said walls of said thermoplastictubular parison are forced together along four said paths.

3. A method according to claim 1 wherein said thermoplastic parison isheated to a temperature near to, but below its crystalline melt point,said thermoplastic still being i a crystalline condition.

4. A method according to claim 3 comprising in addition: closing a moldabout said parison and introducing fluid pressure into the interior ofsaid parison to expand it into conformity with said mold.

1. In a method of blow molding hollow articles by forming a heatedthermoplastic tubular parison, sealing and pinching off an open end ofsaid parison, and expanding said parison to conform to the shape of amold cavity, the improvement comprising: performing said sealing andsevering operation by simultaneously applying pressure radially inwardfrom at least three sharp points thus forcing the walls of said heatedthermoplastic tubular parison together along at least three differentpaths substantially perpendicular to and which have a common junctionnear the longitudinal axis of said heated thermoplastic tubular parisonto thereby obtain a seal having a multi-line configuration, andcontinuing the force along said paths until The lower portion of saidheated thermoplastic tubular parison is pinched off from the resultingsealed upper portion.
 2. The method of claim 1 wherein said walls ofsaid thermoplastic tubular parison are forced together along four saidpaths.
 3. A method according to claim 1 wherein said thermoplasticparison is heated to a temperature near to, but below its crystallinemelt point, said thermoplastic still being in a crystalline condition.4. A method according to claim 3 comprising in addition: closing a moldabout said parison and introducing fluid pressure into the interior ofsaid parison to expand it into conformity with said mold.